1. Field of the Invention
The present invention generally relates to the field of electrical connectors, and in particular to a 90.degree. shear connector in which the contacts are sheared in groups at different times so as to minimize the shear force while maximizing individual contact strengths. The shear connector of the invention is especially suitable for use as an umbilical chord connector for a missile launching device.
2. Description of the Related Art
Electrical connection between a missile about to be launched and a corresponding launching device is conventionally provided by an umbilical chord that extends from the launching device to the missile. The umbilical chord is designed to break away from the missile when the electrical connection is no longer required and before the umbilical chord can interfere with lift off or cause damage to the launching device.
Break-away connectors have been in use for this purpose at least since the 1950's. The Atlas launch vehicle system used in the Mercury manned space program, for example, employed solenoids within the connector that were designed to unmate upon launching, while the Minuteman missile system used pyrotechnic (squib) charges to accomplish disconnection and break-away. Numerous other break-away arrangements have also been proposed or used, including arrangements involving shearing of the connector shell or coupling mechanism to allow the mating contacts to pull away from each other, as well as shear connectors having contacts designed to shear along a predetermined shear plane rather than to pull out of the mating connector during coupling.
As missile systems have become increasingly reliant upon computerized launching devices, the umbilical chord has had to carry greatly increased traffic, resulting in ever increasing contact densities for the umbilical chord connectors. As a result, problems such as shielding, environmental sealing, and prevention of contact shorting during break-away that were adequately addressed by the prior connector arrangements have become more acute, leading to the need for more sophisticated designs. Squib and electro-mechanical release arrangements that served well in the Atlas and Minuteman systems are difficult to implement in the high density connectors necessary for more modern tactical missile systems, while the early shear connector designs utilized contact arrangements entirely unsuitable for missile systems requiring high density data communications.
Two examples of prior shear connector arrangements of the type mentioned above are disclosed in U.S. Pat. Nos. 2,951,421 and 4,863,397. U.S. Pat. No. 2,951,421 describes a connector in which shearing is accomplished by using perforated tape contacts designed to tear apart during launch, while U.S. Pat. No. 4,863,397, designed for a gasoline pump rather than a missile launching device, describes a connector having notches in the shell designed to shear, followed by breaking apart of the contacts along a plane defined by the notches in the shell. Examples of non-shearing break-away connectors for various purposes are also found in U.S. Pat. Nos. 4,138,181, 4,490,002, 4,522,458, and 4,874,316.
Neither of the shear connectors disclosed in U.S. Pat. Nos. 2,951,421 or 4,863,397 is suitable for use in more contemporary missile launch systems. Aside from the problems of lack of adequate shielding and the non-standard nature of the contacts disclosed in U.S. Pat. No. 2,951,421, neither of the shear connectors disclosed in these patents provide sufficient control of the shear forces to ensure a clean break at exactly the right moment during launch. The connector of U.S. Pat. No. 2,951,421 was basically designed for low density power connections, while the gasoline pump connector of U.S. Pat. No. 4,863,397 not only provides a relatively low contact density, but also utilizes a spring to pull the connectors apart following shearing of the connector shell.
In order to better control the shear forces by eliminating reliance on shearing of the connector shell as in U.S. Pat. No. 4,863,397, or reliance solely on perforations in the contacts as in U.S. Pat. No. 2,951,421, and to allow for connector sealing, grounding, and shielding arrangements not required in U.S. Pat. Nos. 4,863,397 and 2,951,421, an improved shear connector corresponding to the one illustrated in FIGS. 7-9 was proposed as part of the program to replace the current RIM-7 Sea Sparrow Missile used by the U.S. and NATO navies. While FIGS. 7-9 are included as background for the present invention, it is to be understood that these figures do not necessary depict "prior art" since the present inventor was also primarily responsible for development of the connector illustrated in FIGS. 7-9, which was never placed into production.
In the connector of FIGS. 7-9, the need for shearing of the plug connector shell 100 is eliminated by terminating the plug connector shell short of the shear plane 101 and by providing a two part plug connector insert 102,103 within the connector shell, the mating or front insert 102 and the rear insert 103 of the connector insert being held together by shear pins 104 integrally molded with front insert 102, inserted into openings 105 in rear insert 103, and secured by an adhesive. To ensure a clean break at the shear plane 101 between the front and rear inserts following shearing of pins 104, the proposed connector also features scoring or notching 106 of the plug connector contacts 107, as shown in FIG. 8, and multiple ramps 108 and corresponding cavities or indents 109 to prevent relative vertical movement of the contacts and possible shorting of missile circuits following shearing.
This design further included various features designed to ensure ground continuity between the plug and receptacle, electromagnetic interference (EMI) shielding, environmental sealing, and ease of initial interconnection of the plug and receptacle, such as a ground strap between the plug connector shell 100 and receptacle connector shell 110. As illustrated in FIG. 9, for example, the plug and receptacle are provided with an O-ring seal 111, a jack screw 112 to secure the front portion 102 of the connector insert to the receptacle by means of a threaded sleeve 113 molded into the receptacle insert 114, and pins 115 extending from the receptacle insert to orient or polarize the plug and receptacle to ensure proper mating of plug connector contacts 107 with receptacle connector contacts 116. Finally, to facilitate assembly, plug connector contacts 107 are divided into two sections to facilitate assembly of the front and rear inserts 102,103, including scored double-ended contact pins 117 molded into the front insert portion 102 and rear contact sleeves 118 fitted into openings 119 in the rear insert portion 103.
While many of the features of the connector illustrated in FIGS. 7-9 have been incorporated into the shear connector of the present invention, preliminary tests on the connector illustrated in FIGS. 7-9 resulted in failure of the connector to shear cleanly at the required minimum force. The problem turned out to lie in the inability to adequately control shearing of the shear pins 104, and the excessive force required to shear all of the contacts 107 at the same time without unduly weakening the contacts.
As a result, a new structure was needed to connect the front insert portion to the rear insert portion in such a way as to enable shearing or breakage of the connection at a predetermined force, and to reduce the amount of force necessary to shear the contacts while providing contacts of sufficient strength. The present invention addresses both of these problems, while still including the features of plug-to-receptacle grounding, EMI protections, O-ring sealing, and ease of interconnection offered by the design illustrated in FIGS. 7-9.